The rejection of faulty tracks on a tape is usually done under conditions which allow regions of marginal performance to go undetected. On subsequent data readouts these regions of marginal performance cause signal dropouts resulting in significant data errors. Signal dropouts are due to such factors as tape contamination or localized imperfections in the magnetic layer of the tape. Such dropouts require re-recording if data errors are to be avoided. Signal dropouts may also occur during successive reading attempts. Thus, even though an error due to signal dropout is detected and re-recording attempted, if adequate read threshold control is not provided successive read attempts may still result in marginal performance.